The present invention relates to a device for collecting layers of fat known as xe2x80x9cfloating matterxe2x80x9d which forms in residual water treatment settling tanks after the flocculation zone. This device is more particularly applicable to settling tanks of rectangular shape.
In such settling tanks, the floating matter is formed either naturally or as the result of degreasing, and the mass of floating matter is greater when it is the result of an in-situ degreasing of the effluent. It is therefore essential for this floating matter to be removed periodically to allow the settling process to continue correctly and also for reasons associated with the aesthetics of the work.
At the present time, use is made of floating matter collection systems which are produced in the form of a partially submerged chute, open at the top, positioned at the end of the tank, and the manual or motorized periodic pivoting of which creates a sheet of water that carries along the floating matter which is then removed from the settling tank by a removal duct.
Under actual conditions of use, these known devices have the following particular drawbacks:
a problem of dynamic sealing between the settling tank and the duct that removes the floating matter, in the region of the chute;
the presence of a significant amount of water accompanying the floating matter, causing this to be diluted, this dilution impeding any downstream treatment of the fats,
haphazard collection of thick floating matter which can only with difficulty be carried along by a shallow sheet of water, and
the difficulty of removing the floating matter in the chute under gravity.
Starting out from this state of the art, the present invention sets out to provide a novel device that allows the drawbacks outlined above to be avoided.
In consequence, the subject of the present invention is a device for collecting floating matter that forms on settling tanks in residual water treatment plants, characterized in that it is in the form of a rotary skimmer fitted above the tank at the end thereof and which comprises:
an emerged flow tube which has a longitudinal slot and which is closed at one end and open at the other;
a submerged, preferably segmented bucket welded to the said flow tube along the entire length of the latter, and
a motor driving the tube plus bucket assembly periodically through 360xc2x0 so that the floating matter is collected on each rotation by the said bucket, whose position with respect to the emerged flow tube is determined so that the said floating matter is poured out into the said tube via its longitudinal slot then removed under gravity through the open end of the said emerged tube.
According to a preferred embodiment of the invention, the drive motor is mounted at one of the ends of the flow tube via a coupling comprising a flange and a system of elastic blocks, and at the other end of the said tube there is a support system consisting of rollers, arranged preferably 120xc2x0 apart.
According to the present invention, there is an inductive sensor that detects the stopping position of the said rotary skimmer, using a metal block provided on the flange coupling the motor to the flow tube.
As a preference, according to the present invention, the device is operated as one complete rotation, followed by a time delay, but this operation may take the form of a number of consecutive rotations, followed by a time delay or of continuous rotation, depending on the desired removal rates. It is possible to provide an automated mechanism for controlling the motor, this being based on an adjustable time delay, setting the period of standby between two floating-matter-collection cycles.
According to another embodiment of the device of the invention, there is a deflector on that wall of the tank along which the said rotary skimmer is mounted, at the height of the level of water in the said tank, so as to avoid any stagnation zone in the zone from which floating matter is taken. This deflector may, for example, be made in the form of an inverted angle bracket.
Other features and advantages of the present invention will become apparent from the description given hereinafter with reference to the appended drawing which illustrates one entirely non-limiting embodiment thereof.